You’ve probably seen fuel credit cards before — ones offering you a discount on petrol purchases if you pay using their credit card. They’re often tied to a specific brand of fuel, like Citibank’s BP credit card. Fuel savings are certainly appealing. But are the deals really worth signing up for a new credit card?

Let’s take a look at both some of the positive and negative sides of fuel credit cards, to help you decide if getting one is the right option for you.

Why Fuel Credit Cards Can be a Good Deal

If you feel like you’re spending too much on petrol, getting a fuel credit card might just seem like a common sense decision. For example, the BP credit card gives you 5% off of your petrol purchases at any BP station. If you use BP frequently (or they’re near you so you can start becoming a customer), it could be a good deal.

The percentage you can save is often higher with a fuel credit card than if you simply used a traditional cash back rewards credit card for those same petrol purchases. Some of these cards also offer savings or cash back on purchases you make elsewhere, although at a lower percentage rate.

Fuel Credit Cards: The Other Side of the Story

There’s another side to the story though. For example, if you don’t have a rewards card yet and you happen to spend a lot on fuel, a fuel credit card could make sense. But if you already have a few credit cards — including rewards cards — it isn’t necessarily as good of an option. Why? Because too many credit cards can make you look like a bigger credit risk down the road (such as when looking for a mortgage), and it might not be worth it if you already have a credit card that will let you save on those purchases.

Everyone’s spending habits are different, so you’ll need to crunch some numbers. Let’s say you tend to use 10% of your total credit card spending each month on petrol. Let’s take a nice round number and say you average $1000 per month — $100 on petrol purchases. Now let’s say you have two options: a rewards credit card offering 1% cash back on all purchases or the BP credit card offering 5% back on petrol and just 0.5% on other purchases.

If you plug in those numbers you’ll find that the 1% cash back offer on everything you buy leads to $10 savings that month, while the fuel credit card saves you slightly less at just $9.50 each month. The rewards card would be the better deal. Factor in how much you tend to spend on fuel now. If you spend significantly more, the fuel card might still make sense.

Another consideration is limits. The BP credit card for example might offer the higher 5% discount rate on fuel, but there’s a limit. You only get the discount on the first $600 you spend at BP locations each statement period. For an average driver that might be fine. But if you’re a heavy spender (such as someone on the road frequently for business) and you’re hoping to save on all of your fuel purchases, you might be disappointed.

Fuel credit cards definitely have their place, and they can help you save money. The key is knowing your other money-saving options as well so you can figure out if what sounds like a good deal on paper is really the deal that’s going to save you the most.